1. Field of the Invention
The present invention relates to a ball mill and, more particularly, to a planetary ball mill of the continuous type, in which a mill pot is fitted inside a mill casing, and fine crushing or pulverization is performed while crushing mediums together with a material to be crushed are sealed.
2. Prior Art
In a planetary ball mill of conventional construction, a plurality of mill pots evenly disposed around a main shaft (i.e., symmetrically in case of two mill pots, or radially from the main shaft with equal distance in case of three mill pots) revolve with the rotation of the main shaft, and these mill pots themselves rotate around their own axis. In the vertical type of planetary ball mill, which in principle is schematically shown in FIGS. 5(A) and (B), the driving force of a motor 6a is transmitted to a main shaft 22a through a sprocket 61a and a transmission chain 62a. A rotary shaft 101 attached to the mill pot 31a is rotatably mounted on a mill body fixed to the main shaft. In the meantime, a sun sprocket 71a fixed onto the same axis as the main shaft so as not to rotate and a planetary sprocket 24a disposed on the rotation shaft are connected to each other by way of a transmission chain so that the mill pot, fixed to the rotary shaft, is turned around by causing the rotary shaft to rotate and revolve.
When putting a crushing medium B and a material S to be crushed in the same mill pot and driving the motor, the mill pot 31a rotates and revolves, whereby the crushing medium performs its proper motion by centrifugal acceleration and crushes the material to be crushed. More specifically, in the rolling ball mill of the conventional type, the ball-shaped crushing medium and the material to be crushed bring about a cascade motion in a rolling cylinder, and the material is crushed as a result of collapse and abrasion due to gravitational drop of the crushing medium. On the other hand, in the planetary ball mill, the crushing speed is remarkably improved by the mutual cooperation between the centrifugal force due to the high speed revolution and rotation and the Coriolis force, whereby fine particles excellent in distribution of particle size can be obtained in a rather short time. In particular, the crushing force due to high speed rotation is remarkable such that, for instance, when putting silica sand of several milimeters in grain size in the mill pot, fine particles of several microns in average size can be obtained just after operating the mill for only a few minutes. When completing the crushing operation, only the mill pot is removed to pick up or recover the produced fine particles from the mill pot.
Other vertical type planetary ball mills have also been heretofore proposed. That is, in the Japanese Laid-Open Patent Publication (unexamined) No. 5-146698, a mill body is formed of a disk, and a mill pot is engagedly fitted in a hole provided through the disk to increase rigidity. In the Japanese Laid-Open Patent Publication (unexamined) No. 4-40245, a hollow part is provided between the mill housing and the mill pot so as to cause a cool or hot fluid to circulate through the hollow part thereby adding a temperature function regulation to the mill. Further, in the Japanese Laid-Open Utility Model Publication (unexamined) No. 4-17837, a planetary ball mill of small noise type is proposed in which the driving force is transmitted to a rotary shaft and a revolving shaft by way of a driven flexible endless belt.
In most of the prior art proposed in the form of a vertical type planetary ball mill, a batch system is employed, and the fact is that there is substantially no continuous system though it is employed in most of the horizontal planetary ball mills. In the batch system, once any material to be crushed is placed in a mill pot, the material is subject to a required crushing operation for a required time by hermetically closing the mill pot with a cover. This means that the batch type may be suitable for small scale crushing, such as experimental crushing, but that it is difficult to free it from the influence of gravity during large scale crushing operation because the mill pot is arranged vertically. As a result, in the batch type, after repeating the same manner of operations continuously for a long time under the sealed state, there arises a disadvantage of particle size nonuniformity or unevenness depending upon the location of the material inside the mill pot. Moreover, when chemical reaction of the material is intended, in addition to crushing, there may arise a further disadvantage of nonuniformity in the quality of the crushed material. As far as uniformity of quality and particle size is concerned, it seems that the continuous circulation type is significantly advantageous because, in this type, it is possible to limit the crushing and reaction time in the mill pot, and recycle (feed again) an intermediate product to the same mill pot. Furthermore, in the conventional vertical ball mill not employing the continuous circulation system, there is a further disadvantage in that the material treated in the mill pot must be discharged for each treatment and then another new material to be treated must be supplied. This leads to troublesome manual work resulting in a considerable influence on efficiency or productivity.
Notwithstanding the above, no continuous vertical planetary ball mill type has been proposed up to today. This is because, in the construction of the vertical type, it is an essential requirement that the strength of the rotating shaft is high as compared with the horizontal type since the rotary shaft is supported as a cantilever in the vertical type while it is supported at the center from two sides in the horizontal type. Moreover, in the horizontal type, it is possible to uniformly and constantly supply the mill pot with material at all times and selectively recover only the fine particles crushed to a required partical size from among the treated material by utilizing continuous air-swept communication to a final bag filter. On the other hand, in the vertical type, there exists an additional problem of gravity, which has never been solved in the prior art.